Recently, as vehicles are electronically controlled, electronic components control various vehicle components such as an engine and a brake. There is an increasing number of electronic control units (ECUs) connected to the electronic components. The ECUs can cooperate and share information with each other and therefore can provide a network (onboard system). The onboard system (in-vehicle system) is connected to an external tool through a connector. Using the external tool, the onboard system can diagnose vehicle states through the ECU or rewrite (reprogram) a program stored in the ECU.
There is a known technology (see patent document 1) that encrypts transmission data in order to improve the security of information to be transmitted. Cryptographic communication between the external tool and the onboard system may prevent an improper access to communication data.
The above-mentioned onboard system may be subject to an improper access (e.g., improper tampering with the ECU program) using an improper external tool.
Patent Document 1: JP-A-2009-81755